The Origin of Capacity Fading in NiFe2O4 Conversion Electrodes for Lithium Ion Batteries Unfolded by 57Fe Mossbauer Spectroscopy

The Li-driven electrochemical conversion reaction is regarded as a promising mechanism for lithium storage in anode materials. Two NiFe2O4 samples have been prepared by a sol gel method at different annealing temperatures. The distinct textural properties were correlated to the electrochemical performance in lithium test cells. Fe-57 Mossbauer spectroscopy was used to evaluate the local environment of metallic iron atoms in the discharged electrodes. The different contributions of core and surface atoms have been correlated to the effect of the annealing temperature and the capacity fading observed during the first cycles. The decrease of the blocking temperature of ferromagnetic-superparamagnetic transition in the discharged electrodes is ascribed to a parallel decrease in the metallic particle size.